1. Field of the Invention
The present invention relates generally to computer modules having a plurality of components mounted on two or more stacked printed circuit boards, and more specifically to high density memory modules using stacked printed circuit boards with heat dissipation structures.
2. Description of the Related Art
Computer systems often utilize modules comprising one or more printed circuit boards (PCBs). Each PCB has one or more components (e.g., integrated circuits or ICs) mounted thereon, and the components can be mounted on one side or on both sides of the PCB. In certain computer systems, the PCBs of the module are stacked next to one another to increase the functionality of the module. For example, board stacking is a method used to increase the memory density in memory subsystems. The technique is also used to increase the device density of other components, such as logic. Stacking enhances the capability of the module, particularly if components are assembled on each of the two sides of each of the stacked PCBs. In such configurations, the components mounted on one side of one PCB are positioned in close proximity to the components mounted on a neighboring side of a neighboring PCB.
Stacking configurations can cause problems due to power dissipation in the components which are in close proximity. Some or all of the components can generate significant amounts of heat, which can raise the temperature of the component itself or of the surrounding components of the module. The narrow air gap between the components on either side of the stacked PCBs prevents air flow which would otherwise keep the components within their specified operating temperature ranges. The raised temperature of these components can have harmful effects on the performance of the components, causing them to malfunction.
Prior art systems utilize heat spreaders to radiate the heat away from the heat-generating component and away from the surrounding components of the module. Such prior art heat spreaders are mounted over the heat-generating components. In stacked configurations, the prior art heat spreaders are typically mounted over components on an outside surface of the PCB (i.e., a surface away from a neighboring PCB). While these prior art heat spreaders can dissipate heat generated by the components on the outside surface of the PCB, components on the inside surfaces would remain hot. In addition, the components on the outside surface of the PCB are effectively cooled by air flowing across the components from a ventilation fan. However, the narrow air gap between the stacked PCBs would allow very little cool air from the ventilation fan to cool the components on the inside surfaces to within the specified operating temperatures.